The invention concerns a method for coiling metal strip with                a coiler mandrel with a mandrel body,        a plurality of radially expandable segments arranged around the mandrel body, and        a plurality of hydraulic cylinders by which the segments can be moved in the radial direction.        
The invention also concerns a device for coiling metal strip.
In rolling mills, metal strip is shaped into sheets or into wound coils to allow transport and further processing of the strip within the mill or at the customer's site. Metal coils are produced by radial coiling of straight metal strip in a coiling installation. The metal strip is a product of a hot strip mill or cold strip mill. This means that the temperature can be less than 100° C. or greater or much greater than 100° C., depending on the type of mill and heat treatment.
Coiling installations operate basically in such a way that the metal strip is guided onto a rotating mandrel, the so-called coiler mandrel. The metal strip is guided around the coiler mandrel by guide elements, such as deflecting shells, guide rollers, belt conveyors, etc., which are arranged around the longitudinal axis of the coiler mandrel in such a way that they can move radially. When, after the start of coiling, the coiler mandrel has been enabled to develop tension in the metal strip, the aforementioned guide elements are moved away, for example, swiveled away, from the metal strip into a neutral position. When necessary, e.g., when the metal strip threatens to lose its tension as it exits, e.g., the rolling stand or the driving equipment of the coiling installation, the guide elements can be swung back in. This prevents the coil from losing its shape or cracking.
A prior-art coiling installation consists, for example, as shown in FIG. 1 and FIG. 2, of:                a motor 1 and a transmission 3, for driving the coiler mandrel,        a clutch 4, which connects the drive with the mandrel,        a rotating or stationary hydraulic cylinder 5, which is connected with an expanding bar 13 or expander unit,        a displacement measuring system for measuring the piston displacement (not shown),        a rear mandrel bearing 6 and a front mandrel bearing 7,        a coiling section 8,        a mandrel body 12, which supports the expanding bar 13 and a pressure member 14,        segments 15, which are held with tongues (not shown) of the mandrel body 12 and are moved in or out by means of the pressure member 14, and        a mandrel step bearing 9.        
The functioning of the prior-art coiler mandrel is shown in greater detail in FIG. 2. During coiling, the metal strip 10 wraps spirally around the coiler mandrel to form windings 11. Coiler mandrels are able to increase or decrease (to expand or contract) their outside dimension 8.1 in the coiling section. This function is realized by moving the outer segments 15 in the radial direction. To start the winding operation, the metal strip 10 is guided around an expanded coiler mandrel. After the metal strip 10 has been coiled into a metal coil, it must be released from the coiler mandrel to allow it to be removed. To this end, the coiler mandrel is contracted, i.e., the segments 15 are moved towards the longitudinal axis of the coiler mandrel, thereby reducing the outside dimension 8.1 of the coiling section 8. The coiler mandrel releases the coil.
The expansion mechanism is illustrated in FIG. 2. The expanding bar 13 has at least one oblique plane 13.1 and preferably several. The movement 13.2 of the expanding bar 13 left or right in the axial direction of the coiler mandrel causes the oblique plane 13.1 to be moved, and the pressure member 14 is raised or lowered in the radial direction and in turn raises or lowers the radially more outwardly located segment 15. Since the segments 15 of the coiling section 8 expand and contract as uniformly as possible and must absorb the forces that arise, several oblique planes are arranged, preferably uniformly, over both the circumference and the length of the coiling section 8. The expanding bar 13 is coupled with the hydraulic cylinder 5, from which it receives a translational drive or a holding force.
A common feature of previously known coiler mandrels is that the segments 15 are moved by means of an oblique plane 13.1. In this regard, it is not necessary that a pressure member 14 takes on the transmission of the force and movement. Oblique planes 13.1 are often joined to the segments 15, so that there is direct contact between the expanding bar 13 and segment 15. In order to hold the segments 15 in the coiler mandrel during rotation against centrifugal force and gravity, brackets, for example, are provided, which are rotatably supported in the expanding bar 13 and rotatably supported in the segments 15. In a different embodiment, the segments 15 can be held in the coiler mandrel by means of guides, against which the segments 15 rest.
Since the expanding bar 13 is mounted inside the mandrel body 12, an opening is provided in the mandrel step bearing 9 for this purpose. The expanding bar 13 is inserted into the mandrel body 12 through this opening. To be able to link the step bearing to the mandrel body 12, a joint 9.1 is provided here. This is preferably realized as a bolted joint.
A coiler mandrel in a hot strip mill can usually be used for coiling metal strip with thicknesses of 0.8 mm to 25.4 mm. In this connection, the strengths can vary between low, e.g., for low carbon, and high, e.g., for pipe grades (X80, X100, etc.). Of course, in a coiler mandrel according to the prior art described above, no systematic and precise force setting can be made. The reason for this is the oblique planes, which, as a result of their high and nonreproducible friction, bring about a corresponding hysteresis. The difficulty of the nonreproducibility of the friction is based on the presence of wear on the pressure member, on the segments and on the expanding bar. The wear takes the form of removal of material, deformation, changes in surface roughness, etc. A complicating factor is that the lubricating conditions can be unfavorable, since, for example, grease cannot emerge due to high pressure on the grease discharge borehole, or the grease burns or carbonizes when high temperatures develop. It is also possible for the grease to be washed away by cooling water. The penetration of dirt and scale also has an unfavorable effect on the sliding surfaces if the dirt and scale contaminate the grease and/or get between the sliding or friction surfaces. The consequence of deformation and removal of material is that the segments are no longer able to move up to the desired outside dimension, i.e., the maximum coiler mandrel diameter and the horizontal position of the segments can no longer be attained. The design of the joint 9.1 for the mandrel step bearing is the deciding factor for the loading capacity of the coiler mandrel. Basically, the joint 9.1 (or point of separation) represents a weak point.
Austrian Patent 219 940 discloses a prior-art device for controlling winding drums, with a drum member and two tightening segments pivotable thereon, on which acts a row of hydraulically operated pistons, pins, or the like, which spread the segments apart. The pistons, pins or the like are supported in the drum member or in a part that is directly or indirectly connected with it. A row of hydraulically operated pistons, pins, or the like acts on each of the two tightening segments between its free end that faces the other tightening segment and its pivoted part. In addition, a thrust segment is provided, which is placed between the tightening segments that have been spread apart.
Other coiler mandrels that have piston-cylinder units for the spreading of segments are disclosed by the documents DE 26 20 926 A1, U.S. Pat. No. 3,273,817, and U.S. Pat. No. 3,414,210.
EP 0 017 675 B1 discloses an expandable coiler mandrel with a core, with a number of radially expandable segments arranged around the core, and for each segment, with a number of hydraulic piston-cylinder units, by which the segments can be moved radially. The segments are connected with the hydraulic units in the core. In addition, the segments are fastened to the pistons of the hydraulic units. The pistons are annular and mounted around pins, which in turn are fastened to the core and have heads for limiting the radial upward movement of the segments. First and second chambers for hydraulic fluid are provided on the radial inside and outside of the pistons, so that the hydraulic units can be actuated to move the segments in and out. The first chambers of the hydraulic units (for moving the segments out) are connected with a number of hydraulic cylinders, whose pistons are arranged for movement together, so that the first chambers assigned to a single segment are each connected with at least two different hydraulic cylinders.
A disadvantage of the previously known coiler mandrels is that the radially extensible cylinders are all hydraulically coupled with one another, i.e., they have a common supply line (pressure line) for at least two, but usually more than two, cylinders. In the known coiler mandrels, only the terminal positions of the cylinders (completely expanded or completely contracted) are ever moved into. Further expansion of the segments from an initial expanded position (intermediate position of the segments) is not possible, because the friction or the load differs from cylinder to cylinder. The cylinders would thus produce variable extension of the segments, and the eye of the coil, which is formed by the outer contour of the coiler mandrel, would not be cylindrically formed. Noncircular formation of this type leads to problems during the further handling of the coil.